For ecological reasons, there is considerable interest, both from the producers and the consumers of emulsion preparations, in W/O emulsifiers which are based on natural raw materials. For this reason, despite their mediocre efficacy, partial esters of polyalcohols, such as glycerol, polyglycerol, sorbitol or methylglycoside, and fatty acids, such as oleic or isostearic acid, are still finding diverse uses.
This type of emulsifier is not suitable, for example, for flowable emulsions (lotions) or for creams with a high content of natural triglycerides. The creams which satisfy the stability requirements of the market (temperature stability of from -15 to +45.degree. C., sometimes from -25 to +50.degree. C.) contain as the oleophilic components largely paraffin oils and fatty acid esters of monoalkanols (MW&lt;500); these have more favorable technological properties than the higher-molecular-weight triglycerides. Nevertheless, for stabilization purposes, relatively high concentrations of viscosity-increasing waxes (.gtoreq.3%) are required, which have an adverse effect on the application properties, since they produce an undesired sticky, greasy feel on the skin.
Coemulsifiers, in particular ethylene oxide adducts in combination with metal soaps, merely broaden the range of applications to paraffin oil-containing lotions.
The emulsifying properties of the polyalcohol-fatty acid partial esters are considerably exceeded by the polyglycerol esters of dimerized and polymerized unsaturated C.sub.18 -fatty acids. They are obtained from the mono-and diglycerides of vegetable oils, preferably soya oil, by thermal treatment at approximately 300.degree. C. over several hours or by transesterification of a thermally polymerized vegetable oil with polyglycerol.
The polyglycerol polyricinoleates formed from castor oil by an analogous process are also effective W/O emulsifiers (DE-B-44 09 659). Because of their sensitivity to oxidation and their pronounced greasy, rancid odour, neither class of substances has been able to establish itself for use in cosmetic or pharmaceutical emulsion preparations. The main factors responsible for this are massive thermal stress during preparation and the unsaturated nature (iodine number approximately 100).
Polyglycerol polyhydroxystearate (Henkel), which is chemically related to polyglycerol polyricinoleate and can likewise be prepared from vegetable raw materials, has, by contrast, a satisfactory sensory quality and in principle is capable of forming cream-like and in particular flowable W/O emulsions.